Wt Widget Gallery

MVC Item Models

A common data model involves lists, tables and trees of more or less uniform items. Several standard widgets provided by the library use such a model. The abstract WAbstractItemModel base class provides the interface which is used by these view classes.

Not only Table Views and Tree Views display (and interact with) data from an item model, but so do also the list-oriented widgets such as Combo box, Selection box, Auto complete, and charting widgets such as Cartesian Chart, Scatter Plot and Pie Chart.

The model

An item model is essentially a table of items, where each item can be a parent to a nested table of items.

Since recursive statements like the one above can confuse even a seasoned programmer, let's start from a simple model, and extend it to more complex instances.

Lists

In its most simple and perhaps most common form, an item model simply stores a list of items. Such a model has only one column.

Each item may holds different facets of the data, stored as different Item Data Roles. If a table has two dimensions (rows an columns), then data roles could be considered as a third dimension.

The common use-case for item data roles is that for a single item, there may be a textual representation, but also an icon, a customized style class, a link, etc...

The built-in views will thus interpret subsets of this data to render a single item. In particular, the following data roles are commonly supported:

DisplayRole: Rendered as text
DecorationRole: Rendered as icons
CheckStateRole: Rendered as check box state
LinkRole: Rendered as links
ToolTipRole: Rendered as tool tips
StyleClassRole: Rendered as style classes

See the WItemDataRole enumeration for a more complete list of standard roles, whose use may depend on the View.

Tables

As a straight forward generalization to lists, tables may include more than one more column, and each item can be identified by a (row, column) pair.

Trees

A tree model is - like a list - a model with a single column. In addition each item may be parent to another list.

At this point it becomes necessary to introduce the concept of a WModelIndex to uniquely identify an item. A model index is a data structucre containing:

row: The row number
column: The column number
parent: The parent model index

The recursion is thus achieved by associating a parent index with each item index. By convention, top-level items have an Invalid index (which is a default constructed WModelIndex). To make the recursive definition consistent, one can also imagine an invisible root item (corresponding to the "invalid" index) which is the parent of the top-level items.

Tree Tables

Finally, a tree table extends the list model by allow additional columns of data to be associated with each item row.

None of the standard Views render hierarchical data that is not present in the first column ! While such data structures can indeed be defined by item models, this will effectively be ignored by the standard View classes.

Top

Standard model implementations

To get you going, and more than sufficient for simple needs, the library provides a number of standard and generic models, which store the data in memory.

WStandardItemModel can implement any kind of item model, being composed of a table of WStandardItem's, which each can contain itself a nested table of WStandardItem items.
WStringListModel only supports lists with a single column, and is thus optimized for list-oriented widgets (combo-boxes and the like).

One particarly useful standard model is the Dbo::QueryModel which is a tabular model backed by database data.

Custom models

Separating models from views would be not very useful, if it were not of the ablity to implement customized models. These could be models that compute some or all data on the fly, or fetch this information from a underlying database or file system, or simply display information from an existing data structure in a tabular/tree-like way.

Table models

As a minimum, a custom table model should reimplement the following methods from WAbstractTableModel:

int rowCount(): Returns the table row count (only for the invalid parent!)
int columnCount(): Returns the table column count (only for the invalid parent!)
boost::any data(): Returns the data for an item, and a particular role
boost::any headerData(): Returns the header data for a column

As an example of a custom table model, consider the following (non-sensical) model that simply displays row/column information for each item.

Example

Column 0	Column 1	Column 2	Column 3	Column 4	Column 5	Column 6	Column 7	Column 8	Column 9	Column 10	Column 11	Column 12	Column 13	Column 14	Column 15	Column 16	Column 17	Column 18	Column 19	Column 20	Column 21	Column 22	Column 23	Column 24	Column 25	Column 26	Column 27	Column 28	Column 29	Column 30	Column 31	Column 32	Column 33	Column 34	Column 35	Column 36	Column 37	Column 38	Column 39	Column 40	Column 41	Column 42	Column 43	Column 44	Column 45	Column 46	Column 47	Column 48	Column 49
Row 0	Item row 0, col 1	Item row 0, col 2	Item row 0, col 3	Item row 0, col 4	Item row 0, col 5	Item row 0, col 6	Item row 0, col 7	Item row 0, col 8	Item row 0, col 9	Item row 0, col 10	Item row 0, col 11	Item row 0, col 12	Item row 0, col 13	Item row 0, col 14	Item row 0, col 15	Item row 0, col 16	Item row 0, col 17	Item row 0, col 18	Item row 0, col 19	Item row 0, col 20	Item row 0, col 21	Item row 0, col 22	Item row 0, col 23	Item row 0, col 24	Item row 0, col 25	Item row 0, col 26	Item row 0, col 27	Item row 0, col 28	Item row 0, col 29	Item row 0, col 30	Item row 0, col 31	Item row 0, col 32	Item row 0, col 33	Item row 0, col 34	Item row 0, col 35	Item row 0, col 36	Item row 0, col 37	Item row 0, col 38	Item row 0, col 39	Item row 0, col 40	Item row 0, col 41	Item row 0, col 42	Item row 0, col 43	Item row 0, col 44	Item row 0, col 45	Item row 0, col 46	Item row 0, col 47	Item row 0, col 48	Item row 0, col 49
Row 1	Item row 1, col 1	Item row 1, col 2	Item row 1, col 3	Item row 1, col 4	Item row 1, col 5	Item row 1, col 6	Item row 1, col 7	Item row 1, col 8	Item row 1, col 9	Item row 1, col 10	Item row 1, col 11	Item row 1, col 12	Item row 1, col 13	Item row 1, col 14	Item row 1, col 15	Item row 1, col 16	Item row 1, col 17	Item row 1, col 18	Item row 1, col 19	Item row 1, col 20	Item row 1, col 21	Item row 1, col 22	Item row 1, col 23	Item row 1, col 24	Item row 1, col 25	Item row 1, col 26	Item row 1, col 27	Item row 1, col 28	Item row 1, col 29	Item row 1, col 30	Item row 1, col 31	Item row 1, col 32	Item row 1, col 33	Item row 1, col 34	Item row 1, col 35	Item row 1, col 36	Item row 1, col 37	Item row 1, col 38	Item row 1, col 39	Item row 1, col 40	Item row 1, col 41	Item row 1, col 42	Item row 1, col 43	Item row 1, col 44	Item row 1, col 45	Item row 1, col 46	Item row 1, col 47	Item row 1, col 48	Item row 1, col 49
Row 2	Item row 2, col 1	Item row 2, col 2	Item row 2, col 3	Item row 2, col 4	Item row 2, col 5	Item row 2, col 6	Item row 2, col 7	Item row 2, col 8	Item row 2, col 9	Item row 2, col 10	Item row 2, col 11	Item row 2, col 12	Item row 2, col 13	Item row 2, col 14	Item row 2, col 15	Item row 2, col 16	Item row 2, col 17	Item row 2, col 18	Item row 2, col 19	Item row 2, col 20	Item row 2, col 21	Item row 2, col 22	Item row 2, col 23	Item row 2, col 24	Item row 2, col 25	Item row 2, col 26	Item row 2, col 27	Item row 2, col 28	Item row 2, col 29	Item row 2, col 30	Item row 2, col 31	Item row 2, col 32	Item row 2, col 33	Item row 2, col 34	Item row 2, col 35	Item row 2, col 36	Item row 2, col 37	Item row 2, col 38	Item row 2, col 39	Item row 2, col 40	Item row 2, col 41	Item row 2, col 42	Item row 2, col 43	Item row 2, col 44	Item row 2, col 45	Item row 2, col 46	Item row 2, col 47	Item row 2, col 48	Item row 2, col 49
Row 3	Item row 3, col 1	Item row 3, col 2	Item row 3, col 3	Item row 3, col 4	Item row 3, col 5	Item row 3, col 6	Item row 3, col 7	Item row 3, col 8	Item row 3, col 9	Item row 3, col 10	Item row 3, col 11	Item row 3, col 12	Item row 3, col 13	Item row 3, col 14	Item row 3, col 15	Item row 3, col 16	Item row 3, col 17	Item row 3, col 18	Item row 3, col 19	Item row 3, col 20	Item row 3, col 21	Item row 3, col 22	Item row 3, col 23	Item row 3, col 24	Item row 3, col 25	Item row 3, col 26	Item row 3, col 27	Item row 3, col 28	Item row 3, col 29	Item row 3, col 30	Item row 3, col 31	Item row 3, col 32	Item row 3, col 33	Item row 3, col 34	Item row 3, col 35	Item row 3, col 36	Item row 3, col 37	Item row 3, col 38	Item row 3, col 39	Item row 3, col 40	Item row 3, col 41	Item row 3, col 42	Item row 3, col 43	Item row 3, col 44	Item row 3, col 45	Item row 3, col 46	Item row 3, col 47	Item row 3, col 48	Item row 3, col 49
Row 4	Item row 4, col 1	Item row 4, col 2	Item row 4, col 3	Item row 4, col 4	Item row 4, col 5	Item row 4, col 6	Item row 4, col 7	Item row 4, col 8	Item row 4, col 9	Item row 4, col 10	Item row 4, col 11	Item row 4, col 12	Item row 4, col 13	Item row 4, col 14	Item row 4, col 15	Item row 4, col 16	Item row 4, col 17	Item row 4, col 18	Item row 4, col 19	Item row 4, col 20	Item row 4, col 21	Item row 4, col 22	Item row 4, col 23	Item row 4, col 24	Item row 4, col 25	Item row 4, col 26	Item row 4, col 27	Item row 4, col 28	Item row 4, col 29	Item row 4, col 30	Item row 4, col 31	Item row 4, col 32	Item row 4, col 33	Item row 4, col 34	Item row 4, col 35	Item row 4, col 36	Item row 4, col 37	Item row 4, col 38	Item row 4, col 39	Item row 4, col 40	Item row 4, col 41	Item row 4, col 42	Item row 4, col 43	Item row 4, col 44	Item row 4, col 45	Item row 4, col 46	Item row 4, col 47	Item row 4, col 48	Item row 4, col 49
Row 5	Item row 5, col 1	Item row 5, col 2	Item row 5, col 3	Item row 5, col 4	Item row 5, col 5	Item row 5, col 6	Item row 5, col 7	Item row 5, col 8	Item row 5, col 9	Item row 5, col 10	Item row 5, col 11	Item row 5, col 12	Item row 5, col 13	Item row 5, col 14	Item row 5, col 15	Item row 5, col 16	Item row 5, col 17	Item row 5, col 18	Item row 5, col 19	Item row 5, col 20	Item row 5, col 21	Item row 5, col 22	Item row 5, col 23	Item row 5, col 24	Item row 5, col 25	Item row 5, col 26	Item row 5, col 27	Item row 5, col 28	Item row 5, col 29	Item row 5, col 30	Item row 5, col 31	Item row 5, col 32	Item row 5, col 33	Item row 5, col 34	Item row 5, col 35	Item row 5, col 36	Item row 5, col 37	Item row 5, col 38	Item row 5, col 39	Item row 5, col 40	Item row 5, col 41	Item row 5, col 42	Item row 5, col 43	Item row 5, col 44	Item row 5, col 45	Item row 5, col 46	Item row 5, col 47	Item row 5, col 48	Item row 5, col 49
Row 6	Item row 6, col 1	Item row 6, col 2	Item row 6, col 3	Item row 6, col 4	Item row 6, col 5	Item row 6, col 6	Item row 6, col 7	Item row 6, col 8	Item row 6, col 9	Item row 6, col 10	Item row 6, col 11	Item row 6, col 12	Item row 6, col 13	Item row 6, col 14	Item row 6, col 15	Item row 6, col 16	Item row 6, col 17	Item row 6, col 18	Item row 6, col 19	Item row 6, col 20	Item row 6, col 21	Item row 6, col 22	Item row 6, col 23	Item row 6, col 24	Item row 6, col 25	Item row 6, col 26	Item row 6, col 27	Item row 6, col 28	Item row 6, col 29	Item row 6, col 30	Item row 6, col 31	Item row 6, col 32	Item row 6, col 33	Item row 6, col 34	Item row 6, col 35	Item row 6, col 36	Item row 6, col 37	Item row 6, col 38	Item row 6, col 39	Item row 6, col 40	Item row 6, col 41	Item row 6, col 42	Item row 6, col 43	Item row 6, col 44	Item row 6, col 45	Item row 6, col 46	Item row 6, col 47	Item row 6, col 48	Item row 6, col 49
Row 7	Item row 7, col 1	Item row 7, col 2	Item row 7, col 3	Item row 7, col 4	Item row 7, col 5	Item row 7, col 6	Item row 7, col 7	Item row 7, col 8	Item row 7, col 9	Item row 7, col 10	Item row 7, col 11	Item row 7, col 12	Item row 7, col 13	Item row 7, col 14	Item row 7, col 15	Item row 7, col 16	Item row 7, col 17	Item row 7, col 18	Item row 7, col 19	Item row 7, col 20	Item row 7, col 21	Item row 7, col 22	Item row 7, col 23	Item row 7, col 24	Item row 7, col 25	Item row 7, col 26	Item row 7, col 27	Item row 7, col 28	Item row 7, col 29	Item row 7, col 30	Item row 7, col 31	Item row 7, col 32	Item row 7, col 33	Item row 7, col 34	Item row 7, col 35	Item row 7, col 36	Item row 7, col 37	Item row 7, col 38	Item row 7, col 39	Item row 7, col 40	Item row 7, col 41	Item row 7, col 42	Item row 7, col 43	Item row 7, col 44	Item row 7, col 45	Item row 7, col 46	Item row 7, col 47	Item row 7, col 48	Item row 7, col 49
Row 8	Item row 8, col 1	Item row 8, col 2	Item row 8, col 3	Item row 8, col 4	Item row 8, col 5	Item row 8, col 6	Item row 8, col 7	Item row 8, col 8	Item row 8, col 9	Item row 8, col 10	Item row 8, col 11	Item row 8, col 12	Item row 8, col 13	Item row 8, col 14	Item row 8, col 15	Item row 8, col 16	Item row 8, col 17	Item row 8, col 18	Item row 8, col 19	Item row 8, col 20	Item row 8, col 21	Item row 8, col 22	Item row 8, col 23	Item row 8, col 24	Item row 8, col 25	Item row 8, col 26	Item row 8, col 27	Item row 8, col 28	Item row 8, col 29	Item row 8, col 30	Item row 8, col 31	Item row 8, col 32	Item row 8, col 33	Item row 8, col 34	Item row 8, col 35	Item row 8, col 36	Item row 8, col 37	Item row 8, col 38	Item row 8, col 39	Item row 8, col 40	Item row 8, col 41	Item row 8, col 42	Item row 8, col 43	Item row 8, col 44	Item row 8, col 45	Item row 8, col 46	Item row 8, col 47	Item row 8, col 48	Item row 8, col 49
Row 9	Item row 9, col 1	Item row 9, col 2	Item row 9, col 3	Item row 9, col 4	Item row 9, col 5	Item row 9, col 6	Item row 9, col 7	Item row 9, col 8	Item row 9, col 9	Item row 9, col 10	Item row 9, col 11	Item row 9, col 12	Item row 9, col 13	Item row 9, col 14	Item row 9, col 15	Item row 9, col 16	Item row 9, col 17	Item row 9, col 18	Item row 9, col 19	Item row 9, col 20	Item row 9, col 21	Item row 9, col 22	Item row 9, col 23	Item row 9, col 24	Item row 9, col 25	Item row 9, col 26	Item row 9, col 27	Item row 9, col 28	Item row 9, col 29	Item row 9, col 30	Item row 9, col 31	Item row 9, col 32	Item row 9, col 33	Item row 9, col 34	Item row 9, col 35	Item row 9, col 36	Item row 9, col 37	Item row 9, col 38	Item row 9, col 39	Item row 9, col 40	Item row 9, col 41	Item row 9, col 42	Item row 9, col 43	Item row 9, col 44	Item row 9, col 45	Item row 9, col 46	Item row 9, col 47	Item row 9, col 48	Item row 9, col 49
Row 10	Item row 10, col 1	Item row 10, col 2	Item row 10, col 3	Item row 10, col 4	Item row 10, col 5	Item row 10, col 6	Item row 10, col 7	Item row 10, col 8	Item row 10, col 9	Item row 10, col 10	Item row 10, col 11	Item row 10, col 12	Item row 10, col 13	Item row 10, col 14	Item row 10, col 15	Item row 10, col 16	Item row 10, col 17	Item row 10, col 18	Item row 10, col 19	Item row 10, col 20	Item row 10, col 21	Item row 10, col 22	Item row 10, col 23	Item row 10, col 24	Item row 10, col 25	Item row 10, col 26	Item row 10, col 27	Item row 10, col 28	Item row 10, col 29	Item row 10, col 30	Item row 10, col 31	Item row 10, col 32	Item row 10, col 33	Item row 10, col 34	Item row 10, col 35	Item row 10, col 36	Item row 10, col 37	Item row 10, col 38	Item row 10, col 39	Item row 10, col 40	Item row 10, col 41	Item row 10, col 42	Item row 10, col 43	Item row 10, col 44	Item row 10, col 45	Item row 10, col 46	Item row 10, col 47	Item row 10, col 48	Item row 10, col 49
Row 11	Item row 11, col 1	Item row 11, col 2	Item row 11, col 3	Item row 11, col 4	Item row 11, col 5	Item row 11, col 6	Item row 11, col 7	Item row 11, col 8	Item row 11, col 9	Item row 11, col 10	Item row 11, col 11	Item row 11, col 12	Item row 11, col 13	Item row 11, col 14	Item row 11, col 15	Item row 11, col 16	Item row 11, col 17	Item row 11, col 18	Item row 11, col 19	Item row 11, col 20	Item row 11, col 21	Item row 11, col 22	Item row 11, col 23	Item row 11, col 24	Item row 11, col 25	Item row 11, col 26	Item row 11, col 27	Item row 11, col 28	Item row 11, col 29	Item row 11, col 30	Item row 11, col 31	Item row 11, col 32	Item row 11, col 33	Item row 11, col 34	Item row 11, col 35	Item row 11, col 36	Item row 11, col 37	Item row 11, col 38	Item row 11, col 39	Item row 11, col 40	Item row 11, col 41	Item row 11, col 42	Item row 11, col 43	Item row 11, col 44	Item row 11, col 45	Item row 11, col 46	Item row 11, col 47	Item row 11, col 48	Item row 11, col 49

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source

#include <Wt/WAbstractTableModel.h>

class VirtualModel : public Wt::WAbstractTableModel
{
public:
  VirtualModel(int rows, int columns)
    : WAbstractTableModel(),
      rows_(rows),
      columns_(columns)
  { }

  virtual int rowCount(const Wt::WModelIndex& parent = Wt::WModelIndex()) const
  {
    if (!parent.isValid())
      return rows_;
    else
      return 0;
  }

  virtual int columnCount(const Wt::WModelIndex& parent = Wt::WModelIndex()) const
  {
    if (!parent.isValid())
      return columns_;
    else
      return 0;
  }

  virtual Wt::cpp17::any data(const Wt::WModelIndex& index, Wt::ItemDataRole role = Wt::ItemDataRole::Display) const
  {
    if (role == Wt::ItemDataRole::Display) {
      if (index.column() == 0)
        return Wt::WString("Row {1}").arg(index.row());
      else
        return Wt::WString("Item row {1}, col {2}")
	  .arg(index.row()).arg(index.column());
    } else {
      return Wt::cpp17::any();
    }
  }

  virtual Wt::cpp17::any headerData(int section,
                                Wt::Orientation orientation = Wt::Orientation::Horizontal,
                                Wt::ItemDataRole role = Wt::ItemDataRole::Display) const
  {
    if (orientation == Wt::Orientation::Horizontal) {
      if (role == Wt::ItemDataRole::Display) {
        return Wt::WString("Column {1}").arg(section);
      } else {
        return Wt::cpp17::any();
      }
    } else
      return Wt::cpp17::any();
  }

private:
  int rows_, columns_;
};

Note The instantiation of this model with a Table View is discussed in MVC Table Views.

Tree models

A custom tree model involves considerably more work. Each internal item (in the first column) which has children, needs to be identified by a unique 64-bit value (which may thus be a long long or a void * pointer). Depending on the source data, a suitable choice must be made for this data.

The following methods must be implemented for a minimally compliant hierarchical model:

int rowCount(): Returns the item children count
int columnCount(): Returns the column count (which is usually the same for each item in the first column)
boost::any data(): Returns the data for an item, and a particular role
boost::any headerData(): Returns the header data for a column
WModelIndex child(): Creates a child index
WModelIndex parent(): Creates a parent index

As an example of a tree table model, consider the following model that loads information from a git repository (in this case, Wt's git). Only a minimum of information is kept in memory: we allocate a data structure only for folders that are being expanded, for use as internal pointer data in model indexes.

Example

Type

File

.editorconfig
.gitignore
Text
CMakeLists.txt
Changelog
Doxyfile
INSTALL
INSTALL.html
INSTALL.win32.html
LICENSE
Markdown
README.md
ReleaseNotes.html
WConfig.h.in
WtInstall.cmake
Folder
cmake/
Folder
doc/
Folder
examples/
Folder
jenkins/
Folder
migrate/
Folder
resources/
Folder
selenium/

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#include <Wt/WAbstractItemModel.h>

#include "Git.h"

class GitModel : public Wt::WAbstractItemModel
{
public:
    /*
     * A custom role for the file contents of a Git BLOB object.
     */
    static constexpr Wt::ItemDataRole ContentsRole = Wt::ItemDataRole::User + 1;

    GitModel(const std::string& repository)
        : WAbstractItemModel()
    { 
	git_.setRepositoryPath(repository);
	loadRevision("master");
    }

    void loadRevision(const std::string& revName) {
	Git::ObjectId treeRoot = git_.getCommitTree(revName);

	layoutAboutToBeChanged().emit(); // Invalidates model indexes

	treeData_.clear();
	childPointer_.clear();

	/*
	 * This stores the tree root as treeData_[0]
	 */
	treeData_.push_back(Tree(-1, -1, treeRoot, git_.treeSize(treeRoot)));

	layoutChanged().emit();
    }

    virtual Wt::WModelIndex parent(const Wt::WModelIndex& index) const {
	if (!index.isValid() || index.internalId() == 0) {
	    return Wt::WModelIndex(); // treeData_[0] is the tree root
	} else {
	    const Tree& item = treeData_[index.internalId()];
	    return createIndex(item.index(), 0, item.parentId());
	}
    }

    virtual Wt::WModelIndex index(int row, int column,
                                  const Wt::WModelIndex& parent = Wt::WModelIndex()) const {
	int parentId;

	if (!parent.isValid())
	    parentId = 0;
	else {
	    int grandParentId = parent.internalId();
	    parentId = getTreeId(grandParentId, parent.row());
	}

	return createIndex(row, column, parentId);
    }

    virtual int columnCount(const Wt::WModelIndex& parent = Wt::WModelIndex()) const {
	return 2;
    }

    virtual int rowCount(const Wt::WModelIndex& parent = Wt::WModelIndex()) const {
	int treeId;

	if (parent.isValid()) {
	    if (parent.column() != 0)
		return 0;
	    Git::Object o = getObject(parent);
	    if (o.type == Git::Tree) { // is a folder
		treeId = getTreeId(parent.internalId(), parent.row());
	    } else                     // is a file
		return 0;
	} else {
	    treeId = 0;
	}

	return treeData_[treeId].rowCount();
    }

    virtual Wt::cpp17::any data(const Wt::WModelIndex& index, Wt::ItemDataRole role = Wt::ItemDataRole::Display) const {
	if (!index.isValid())
	    return Wt::cpp17::any();

	Git::Object object = getObject(index);

	switch (index.column()) {
	case 0:
	    if (role == Wt::ItemDataRole::Display) {
		if (object.type == Git::Tree)
		    return object.name + '/';
		else
		    return object.name;
	    } else if (role == Wt::ItemDataRole::Decoration) {
		if (object.type == Git::Blob)
		    return std::string("icons/git-blob.png");
		else if (object.type == Git::Tree)
		    return std::string("icons/git-tree.png");
	    } else if (role == ContentsRole) {
		if (object.type == Git::Blob)
		    return git_.catFile(object.id);
	    }

	    break;
	case 1:
	    if (role == Wt::ItemDataRole::Display) {
		if (object.type == Git::Tree)
		    return std::string("Folder");
		else {
		    std::string suffix = getSuffix(object.name);

		    if (suffix == "C" || suffix == "cpp")
			return std::string("C++ Source");
		    else if (suffix == "h" || 
			     (suffix == "" && !topLevel(index)))
			return std::string("C++ Header");
		    else if (suffix == "css")
			return std::string("CSS Stylesheet");
		    else if (suffix == "js")
			return std::string("JavaScript Source");
		    else if (suffix == "md")
			return std::string("Markdown");
		    else if (suffix == "png" || suffix == "gif")
			return std::string("Image");
		    else if (suffix == "txt")
			return std::string("Text");
		    else
			return Wt::cpp17::any();
		}
	    }
	}

        return Wt::cpp17::any();
    }
  
    virtual Wt::cpp17::any headerData(int section,
                                  Wt::Orientation orientation = Wt::Orientation::Horizontal,
                                  Wt::ItemDataRole role = Wt::ItemDataRole::Display) const {
        if (orientation == Wt::Orientation::Horizontal && role == Wt::ItemDataRole::Display) {
	    switch (section) {
	    case 0:
		return std::string("File");
	    case 1:
		return std::string("Type");
	    default:
		return Wt::cpp17::any();
	    }
	} else
	    return Wt::cpp17::any();
    }

private:
    Git git_;

    /*
     * Identifies a folder given parent and index
     */
    struct ChildIndex {
	int parentId;
	int index;

	ChildIndex(int aParent, int anIndex)
	    : parentId(aParent), index(anIndex) { }

	bool operator< (const ChildIndex& other) const {
	    if (parentId < other.parentId)
		return true;
	    else if (parentId > other.parentId)
		return false;
	    else return index < other.index;
	}

	bool equals(Wt::cpp17::any o) {
	    ChildIndex *other = Wt::cpp17::any_cast<ChildIndex *>(o);
	    return parentId == other->parentId &&
	        index == other->index;
	}

        int hashCode() {
	    int hash = 1;
	    hash = hash * 31 + parentId;
	    hash = hash * 31 + index;
	    return hash;
	}
    };

    /*
     * Data to be stored for an (expanded) folder
     */
    class Tree {
    public:
	Tree(int parentId, int index, const Git::ObjectId& object, int rowCount)
	    : index_(parentId, index),
	      treeObject_(object),
	      rowCount_(rowCount)
	{ }

	int parentId() const { return index_.parentId; }
	int index() const { return index_.index; }
	const Git::ObjectId& treeObject() const { return treeObject_; }
	int rowCount() const { return rowCount_; }

    private:
	ChildIndex    index_;
	Git::ObjectId treeObject_;
	int           rowCount_;
    };

    typedef std::map<ChildIndex, int> ChildPointerMap;

    /*
     * Expanded folder data
     */
    mutable std::vector<Tree> treeData_;

    /*
     * Indexes into treeData_
     */
    mutable ChildPointerMap childPointer_;

    /*
     * Gets or allocates an id for a folder.
     */
    int getTreeId(int parentId, int childIndex) const {
	ChildIndex index(parentId, childIndex);

	ChildPointerMap::const_iterator i = childPointer_.find(index);
	if (i == childPointer_.end()) {
	    const Tree& parentItem = treeData_[parentId];
	    Git::Object o = git_.treeGetObject(parentItem.treeObject(), childIndex);
 
	    treeData_.push_back(Tree(parentId, childIndex, o.id,
				     git_.treeSize(o.id)));
	    int result = treeData_.size() - 1;
	    childPointer_[index] = result;
	    return result;
	} else
	    return i->second;
    }

    /*
     * Gets the Git::Object that corresponds to an index.
     */
    Git::Object getObject(const Wt::WModelIndex& index) const {
	int parentId = index.internalId();
	const Tree& parentItem = treeData_[parentId];
	return git_.treeGetObject(parentItem.treeObject(), index.row());
    }

    static std::string getSuffix(const std::string& fileName) {
	std::size_t dot = fileName.rfind('.');
	if (dot == std::string::npos)
	    return "";
	else
	    return fileName.substr(dot + 1);
    }

    bool topLevel(const Wt::WModelIndex& index) const {
	return !parent(index).isValid();
    }
};

constexpr Wt::ItemDataRole GitModel::ContentsRole;

Note The instantiation of this model with a Tree View is discussed in MVC Tree Views.

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Sorting

A model may support sorting by one of its columns. This sorting can be implemented within the model itself.

void sort(): Sorts the model according to one of its columns.

Sorting may be bolted onto a source model using the WSortFilterProxyModel, which is one of the standard proxy models.

Model Changes

A model does not necessarily need to be a static data source, but its data can also change, and data (rows/columns) can be added or removed. A model needs to generate events to inform Views of these modifications (for the events to which a View is subscribed). When implementing a custom model which is dynamic in nature, it is therefore important to emit these signals when making the modifications.

Editing

The model API also provides a standard interface to perform editing of the data, and some Views (such as the Tree View and Table Views) can be configured to allow editing of the data.

If a custom wants to support this editing API, it needs to reimplement the following methods from WAbstractTableModel:

bool setData(): Updates data. Views typically use the EditRole for the data used in editing
bool insertColumns(): Inserts one or more columns
bool insertRows(): Inserts one or more rows
bool removeColumns(): Removes one or more columns
bool removeRows(): Removes one or more rows

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